AFAIK the auto-logout was originally to reduce the load on the servers, by removing people who weren't doing anything. As the runescape player base grew enough to 'fill' a server it because useful in that it removed inactive people from a full server to let others in. There seems to be a common misconception here that the logout timer is what logs you out if you accidentally close the window, Not True. This was explained in a previous post - you close the window, it severs the link, you are logged. The exception to this is if you are in combat, you will be artificially kept logged in. This was to combat x-logging in pvp. (Would be great if someone could confirm that, I'm not 100%). Also, you won't keep your gravestone if you log out, a grave disappears prematurely if you log out.